1. Field of the Invention
The present invention relates to a method for measuring the position, attitude and/or positional or attitudinal change of a fixed body in space, and in particular for measuring the position, attitude and/or positional or attitudinal change of the lower jaw of a patient undergoing a dental examination.
2. Description of the Prior Art
An apparatus as disclosed in U.S. Pat. No. 4,371,836 having a magnetic field generator which generates a defined irregular field and a plurality of pickups disposed at an interval from the field generator, the pickups having field flux-dependent sensor elements for sensing the field flux or a change in the field flux. An electronic circuit evaluates the signals from the sensor. The reference points for the pickups are disposed so as to form the corner points of a cube, and the field generator is disposed within the volume defined by the cube. In order to eliminate the influence of external interference fields, the signals of two parallel surfaces of the cube are supplied to adding amplifiers which form two surface signals therefrom which, combined in a differential amplifier, provide twice the useful signal as well as an interference signal compensated to zero.
Despite these measures, field distortions resulting, for example, from the earth's magnetic field or from ferromagnetic materials which may be introduced into or close to the antenna range, cause an incomplete compensation and thus impairment of the entire measuring procedure. In this known apparatus, this problem primarily results from the fact that the signal evaluation for eliminating the interference signal is related exclusively to the antennae themselves, however, interference from other sources within the measuring range remain substantially uncompensated.